Electric communication



y 1942- w. 1.. BARROW 2,281,552

ELECTRIC COMMUNICATION Filed Oct. 51) 1938 BY e; h

ATTORNEY.

Patented May 5, 1942 ELECTRIC COMMUNICATION Wilmer Lanier Barrow, Newton, Mass., assignor to Research Corporation, corporation of New York New York, N. Y., a

' Application October :1, 1938, Serial No. 237,933

14 Claims.

The present invention relates to electric communication and, more particularly, to the propagation or transmission of electromagnetic waves at ultra-high frequencies. From a still more specific point of view, the invention has to do with the propagation or transmission of ultrahigh-frequency waves through hollow conducting pipes or tubes.

In my article, entitled, Transmission of electromagnetic waves in hollow tubes of metal, Proceedings of the Institute of Radio Engineers, October, 1936, p. 1298, there is disclosed a hollowpipe system comprising a hollow pipe or tube and a terminal device at each end of the pipe or tube. The hollow pipe or tube may be of metal, or it may be otherwise provided with an inner conducting wall, and it may contain air or other gas, or liquid or solid dielectrics, or it may be evacuated. The pipe constitutes a uni-conductor, and no return conductor is needed.

Depending upon the type of wave to be transmitted through hollow-pipe conductors of the above-described character, as hereinafter explained, they will have different cross-sectional shapes, sometimes of substantial dimensions.

An object of the present invention is to provide a new and improved hollow-pipe conductor of the above-described character that shall be endowed with the attribute of greater compactness.

Another object is to provide a more compact hollow-pipe conductor of the above-described character, particularly designed for the transmission of waves of the lowest order, designated by Ho,1.

A further object is to provide a novel longitudinally partitioned hollow pipe.

Other and further objects will be described hereinafter and will be particularly pointed out in the appended claims.

The invention will now be described in connection with the accompanying drawing,in which Fig-1 is a diagrammatic perspective, partly in transverse section, of a hollow conducting pipe embodying the present invention; Figs. 2, 3 and 4 are similar views of'modified arrangements; Fig. 5 is an explanatory diagram; and Fig. 6 is a perspective similar to Figs. 1 to 4 of a further modification.

As described in the said article, modulated high-frequency energy may be brought into a sending-end apparatus, at a sending or transmitting station, over a pair of conductors. The sending-end apparatus may comprise appropriate ultra-high-frequency generating, controlling and modulating equipment of any well known character. The modulated ultra-high-frequency energy is taken from the sending-end apparatus and delivered, by means of output terminal conductors, to the sending end of a hollow conducting pipe or tube. The ultra-high-frequency energy is transmitted through the inside or the interior of the hollow pipe, along the direction of its axis, to the receiving end of the pipe, where it is delivered to input terminal conductors of a receiving apparatus at a receiving station of any desired construction. At the receiving station, the signal comprising the intelligence, after recovery by demodulation, may be conducted to its intended terminus. No second conductor is needed within or without the pipefor providing a return connection, as in the conventional twoconductor systems. The pipe may be of circular or any other desired cross-sectional shape, such as elliptical, square or rectangular.

The shape of the lines of electric and of magnetic force into which may be resolved the electromagnetic wave that is transmitted down through the'interior of the pipe and along its inner conducting surface depends upon the material-and the shape of the cross-section of the pipe, the configuration of the terminal device and the frequency of the transmitted wave.

As explained in the said article, there is a minimum or critical frequency for each type of wave below which it cannot exist in, and cannot be transmitted through, the hollow pipe. This critical frequency is different for each type of wave and for different pipe materials, shapes and cross-dimensions. For one type of wave, in pipes of certain cross-sections, the critical frequency is determined by a single dimension of the pipe at right angles to the direction of polarization of the electric field intensity, transverse to the direction of propagation. In a pipe of rectangular cross section, for example, the critical frequency of the Hon wave, which is a wave having only a vertical or transverse component of electric field intensity, depends only on the width of the horizontal sides, and is given by the expression in is the critical frequency,

0 is the velocity of light in unconfined space, in a medium the same as the medium inside the pipe, and

b is the width of the horizontal sides.

From the standpoint of obtaining a. low critical frequency for a, given amount of metal and other material 4n the pipe, it is preferable to make the cross section relatively flat, providing a large value of b.

A pipe, such as is illustrated at 1 in Fig. 5, may, therefore, for some typesof waves, be excessively wide, as indicated at b, the dimension of the oppositely disposed to the thickness of the pipe, represented by the oppositely disposed end walls l3 and I5. For simplicity, the pipe 1 is shown in Fig. 5 as flat, and as of rectangular cross section. The direction of transmission of the waves through the pipe 1 is along the length dimension of the pipe 1, at right angles, or transverse, to the width dimension b and to the thickness dimension of the pipe. Other cross-sectional shapes proposed previously also have the objection that the largest cross-sectional dimension must be of the same order of magnitude as the wavelength. This common objection to the hollow pipes proposed heretofore puts a practical limitation on their usefulness.

To render the exceedingly flat pipe more compact, according to a feature of the present invention, the walls of the hollow pipe 1 may be curved, bent or otherwise distorted in a lateral direction, or transverse to the direction of propagation of the waves through the pipe. The wall 9 of the rectangular pipe 1 may thus become spirally bent or constricted into an inner wall, as shown at ill in Fig. 1, and the wall l9 of the rectangular pipe 1 may become spirally stretched into an outer wall, as illustrated at ll, into substantially concentric spiral arcs, and the ends 13 and 15 of the thus-curved rectangle will become disposed substantially along radii H or of these concentric arcs. A compact rolled pipe or tube is thus provided with oppositely disposed curved walls I0 and H joined together at their ends by the oppositely disposed walls l3 and 15 that are disposed adjacent to each other, as shown in Fig. 1. The are over which the spiral of Fig. 1 extends need not be so great as shown; it may be as small as more than ninety degrees, but it may be sub-.

stantially 180 or 360 degrees, or any other desired value. Neither is it essential that the spiral curve have any particular geometric form; a wide variety of forms will be found suitable.

A small exciting or absorbing rod 2| may be introduced into the pipe, connected by conductors 23, of a coaxial-wire arrangement, or other connecting lines, to suitable transmitting or receiving apparatus. This rod may terminate inside the pipe without making contact with the walls of the pipes as shown in Figs. 1 and 6, or it may terminate on one of the interior walls of the pipe, as shown at 22 in Fig. 2.

In the pipe of Fig. 1, there will be a type of wave corresponding to the above-referred to Hm wave of a rectangular pipe, which will also be called an Hon wave in the curved pipe. There is side walls 9 and 19, with respect substantially only one component of electric intensity in this wave in the pipe of Fig. 1 and it is directed radially. In this type of wave, the critical frequency will be c/2b; that is, the critical wavelength will be twice b, where, in this case, b denotes the curved cross-sectional length indicated in Fig. 1.

In some cases, the oppositely disposed rolled sides I!) and II of the curved rectangle may be connected by a metal strip or strips, which may be radially disposed. According to the embodiment of the invention illustrated in Fig. 2, two substantially concentric metal pipes or tubes 21 and 29, one within the other, in the form, more or less, of a coaxial-pipe system. may be connected or Joined together throughout their length, by means of a metal-wall vane, strip or partition 3|, to constitute a unitary hollow-pipe structure embodying the invention. This structure may be in the form of a cable. A cylindrical relatively short-wave or high-frequency hollowpipe circuit is thus provided in the inner pipe 21, and a relatively long-wave circuit is provided in the space between the continuous oppositely disposed substantially circular pipe walls 21 and 29. The exciting or absorbing rod 2| may bedisposed in the long-wave circuit, as at 22, and another exciting rod or rods may be provided in the usual manner inside the pipe 21.

The connecting vane 3| may, in one modification, be constructed so as to spiral about the axis of the tubes 21 and 29. This modification lends itself well to the construction of flexible cable of this particular type.

For some types of waves, the waves will be the same if the pipes are provided with two such conducting strips or partitions 3| and 33, degrees away from each other, in a common plane, as illustrated in Fig. 6. A semi-circular conductor, comprising half-sections of the pipes 21 and 29 and terminal walls 3| and 33, would be equally effective. The arc should, as before stated, ex-

In a pipe of the character of Fig. 2, the operating wave-length may be about three times as long as would be obtained with the same size of outer conductor 29, but with no inner conductors 21, 3|. Although resembling the coaxial-line structure, the hollow pipes of Figs. 2 and 6 differ fundamentally therefrom, in that the inner metal conductor 21 and the outer metal conductor 29 are connected throughout their lengths by the conducting wall 31 or the conducting walls 3| and 33, respectively. Similar remarks apply to the walls I3 and 15 of Fig. 1. The use of the metal connecting member or membersl3, I6, 31 and 33 obviates the use of dielectric material or spacers for supporting the inner pipe or tube conductor 10 or 21, and may be used as an inner supporting means for rigidly supporting the inner part of the structure. It is not necessary conductively to insulate the individual pipes I0 and II or 21 and 29 from each other, or from critical wave-length, by means of alternately disposed conducting barrier-vane walls 32, 31 and 35,,projecting inward from the respective oppositely disposed walls l3 and ill of the rectangle toward the opposite walls, as shown in Fig. 3. The inner faces of the walls 13 and I5 become thus zig-zagged, suggesting a so-called "folded construction.

A zig-zag path between the substantially parallel'walls l3 and I5 is thus provided from the wall l3, between the walls 9 and32, around bethe wall It and the free end 34 of the wall -41,

between the walls I! and 35, around between the wall l and the free end 44 of the wall 35, and

between the walls 35 and I8, back to the wall it. A folded" pipe or tube of this character, provided with three partitions 32 and 35 and two partitions 31, about three inches along the dimensions indicated by the side walls 8 and I9, and two inches along the end walls l3 and It, was found to have a critical wave-length of about 50 centimeters. The effective length of the "long side" of this experimental pipe was about eleven inches. The corresponding wave-length for an "unfolded rectangle, with a long side of eleven inches, wouldhave been about 55 centimeters.

. The apparatus of Fig. 3 is shown provided with a parallel-wire arrangement 59, l I, leading to an antenna 13. It will be understood that this arrangement, like the coaxial arrangement 23, .25, with the exciting rod 2|, may be employed in any of the modifications.

. A modified construction of the character illustrated in Fig. 3 is illustrated in Fig. 4, where the wall I5 is shown replacedby two semi-circularly arranged half-walls 39 and 4|, integrally joined together at 43, with a wall 45 extending from the junction '43 toward the wall iii. The walls 9, 39 and 45 and the walls 45, 4| and I9 constitute a series of two adjacently disposed U's. Similarly shaped half-pipe portions 45, 46, having ends 49 and 5|, and 41, 48, having ends 55, 53, and respectively joined by semicircularly curved walls 50 and 52, may be disposed in the respective portions 9, 39, 43, 45 and d5, 43, 4|, I9, with the ends 49, 5| and 53, 55, respectively joined to the wall l3. The wall 9, 39, 4|, l9 conforms in shape to and is spaced from, the series of two adjacently disposed Us 45, 50, 46 and 48, 52, 41. The same zig-zag path described above in connection with Fig. 3 is thus provided, extending from the wall 13, between the walls 9 and 45, the walls 39 and 50, and the walls 45 and 45, around between the wall It and the free end 55 of the wall 45, and between the walls 45 and 48, the walls 4| and 52, and the walls 41 and I9, back to the wall IS.

The pipes need not be rigid; they may be flexible, in order that they may be bent to any desired shape; and a plurality of pipe parts or sections may be connected together, as an illustration, by a continuous union between the free end of one or more sections with one of the free ends of one or more other sections.

For the transmission of wave-lengths of about ten or fifteen centimeters, the conductors needed will probably not be larger in cross-section than ordinary electric-line cable.

Further modifications will occur to persons;

skilled in the art without departing from the spirit and scope of the invention, as defined in the appended claims.

What is claimed is:

1. A hollow pipe for the transmission of ultrahigh-frequency waves, the pipe being bounded by oppositely disposed walls and wallsv joining the oppositely disposed walls at their ends, the inner faces of the walls being conducting, at least portions of the oppositely disposed walls curving in directionstransverseto the direction of longitudinal extension of the pipe over an arc of more than ninety degrees,and means for generating -within the pipe, for transmission therethrough, in the direction of the said longitudinal extension, electromagnetic waves of such being disposed adjacent to each characteristic fieldpattern that they are propagated only at frequencies exceeding a critical frequency dependent on the dimensions of the pipe transverse to the said direction of longitudinal extension.

2. A hollow pipe for the transmission or ultra- 1 therethrough, in the direction of the said longitudinal extension, electromagnetic waves of such characteristic'field pattern that they are propagated only at frequencies exceeding a critical frequency dependent on the dimensions of the pipe transverse to the said direction of longitudinal extension.

3. A hollow pipe for the transmission of ultrahigh-frequency waves, the pipe being bounded by oppositely disposed walls and walls joining the oppositely disposed walls at their ends, the inner faces of the walls being conducting, at least portions, of the oppositely disposed walls curving in directions transverse to the direction of longitudinal extension of the pipe over an arc of at least substantially 360 degrees, and means for generating within the pipe, for transmission therethrough, in the direction of the said longitudinal extension, electromagnetic waves of such characteristic field pattern that they are propagated only at frequencies exceeding a critical frequency dependent onthe dimensions of the pipe transverse to the said direction of longitudinal extension.

4. A hollow pipe for the transmission of ultrahigh-frequency waves, the pipe being bounded by oppositely disposed walls and walls joining the oppositely disposed walls at their ends, the inner faces of the walls being conducting, at least portions of the oppositely disposed walls curving in directions transverse to the direction of longitudinal extension of the pipe 'over an arc of at least substantially degrees, the joining walls being disposed adjacent to each other, and means for generating within the pipe, for transmission therethrough, in the direction of the said longitudinal extension, electromagnetic waves of such characteristic field pattern that they are propagated only at frequencies exceeding a critical frequency dependent on thedimensions of the pipe transverse to the said direction of longitudinal extension.

5. A hollow high-frequency waves, the pipe being bounded by oppositely disposed walls and walls joining the oppositely disposed walls at their ends, the inner faces of the walls being conducting, at least portions of the oppositely disposed walls 'curving in directions transverse to the direction of longitudinal extension of the pipe over an arc of at least substantially 360 degrees, the Joining walls other, and means for generating within the pipe, for transmission therethrough, in the direction of the said longitudinal extension, electromagnetic waves of such characteristic field pattern that they are propagated only at frequencies exceeding a critical frequency dependent on the dimensions of the pipe transverse to the said direction of longitudinal extension.

degrees, and means. for

pipe for the transmission of ultra- 8. A hollow pipe for the transmission of ultrahigh-frequency waves of rolled rectangular crosssectional shape, the inner faces of the rolled rectangle being conducting, and means for generating within the pipe, for longitudinal transmission therethrough, electromagnetic waves of such characteristic field pattern that they are propagated only at frequencies exceeding a critical frequency dependent on the dimensions of the said cross-sectional shape.

7. A hollow pipe for the transmission of ultrahigh-frequency waves of rolled exceedingly flat rectangular cross-sectional shape, the inner faces of the rolled rectangle being conducting, and means for generating within the pipe,-for longitudinal transmission therethrough, electromagnetic waves of such characteristic field pattern that they are propagated only at frequencies exceeding a critical frequency dependent on the dimensions of the said cross-sectional shape.

8. A hollow pipe for the transmission of ultrahigh-frequency waves of spiral cross-sectional shape, the inner faces of the pipe being con- .ducting, and means for generating within the pipeffor longitudinal transmission therethrough, electromagentic waves of such characteristic field pattern that they are propagated only at frequencies exceeding a critical frequency dependent on the dimensions of the pipe transverse to the direction of propagation of the waves through the pipe.

9. A hollow pipe for the transmission of ultra,- high-frequency waves of folded rectangular crosssectional shape, the innenfaces of the folded rectangle being conducting, and means for generating within the pipe, for longitudinal transmission therethrough, electromagnetic waves of such characteristic field pattern that they are propagated only at frequencies exceeding a critical frequency dependent on the dimensions of the said cross-sectional shape.

10. A hollow pipe for the transmission of ultrahigh-frequency waves of folded exceedingly fiat rectangular cross-sectional shape, the inner faces of the foldedrectangle being conducting, and means for generating within the pipe, for longitudinal transmission therethrough, electromagnetic waves of such characteristic field pattern that they are propagated only at frequencies exceeding a critical frequency dependent on the dimensions of the said cross-sectional shape.

11. A hollow pipe for the propagation therein of the lowest-order, Ho,1, waves having the electric intensity transverse to the direction of propagation in the pipe, the pipe being of rolled rectangular crosssectional shape, the said waves being capable of propagation through the pipe only at frequency exceeding a critical frequency two oppositely the oppositely disposed walls 2,2a1,os2

where v J 1 c is the velocity of light in unconfined space in medium the same as the medium in the pipe, and

b is the curved cross-sectional length of the rolled rectangle.

12. A hollow pipe for the transmission ofultrahigh-frequency waves, the pipe being bounded by two oppositely disposed walls and walls joining at their ends, the inner faces of the walls being conducting, the oppositely disposed walls being rolled in directions transverse to the direction of longitudinal extension of the pipe over an arc of more than ninety degrees, and means for generating within the pipe, for transmission therethrough, in the direction of the said longitudinal extension, electromagnetic waves of such characteristic field pattern that they are propagated only at frequencies exceeding a critical frequency dependent on the dimensions of the pipe transverse to the said direction of longitudinal extension.

13. A hollow pipe for the transmission of ultrahigh-frequency waves, the pipe being bounded by disposed substantially equally spaced walls and walls joining the oppositely disposed walls at their ends, the inner faces of the walls being conducting, the oppositely disposed walls being rolled in directions transverse to the direction of longitudinal extension of the pipe over an arc of atleast substantially one hundred and eighty degrees, and means for generating within the pipe, for transmission therethrough, in the direction of the said longitudinal extension, electromagnetic waves of such characteristic field pattern that they are propagated only at frequencies exceeding a critical frequency dependent on the dimensions of the pipe transverse to the said direction of longitudinal extension.

14. A hollow pipe for the transmission of ultrahigh-frequency waves, the pipe being bounded by two oppositely disposed substantially equally spaced .walls and walls joining the oppositely disposed walls at their engls, the inner faces of the walls being conducting, the oppositely disposed walls being rolled in directions transverse to the direction of longitudinal extension of the pipe over an arc of at least substantially three hundred and sixty degrees, and means for generating within the pipe, for transmission therethrough, in the direction of the said longitudinal extension, electromagnetic waves of such characteristic field pattern that they are propagated only at frequencies exceeding a critical frequency 

